/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/Parameterization/MeshPlanarSymmetry.h
Note performance of vertex hashing is much better when VertexHashCellSize is large enough that most hash lookups only need to look at a single cell.
static constexpr double VertexHashCellSizeFactor = MatchVertexToleranceFactor * 10;